The present invention relates to a magnetron, and more particularly to an improved filter structure for preventing leakage of undesired electromagnetic waves of certain wavelengths generated by the magnetron such as harmonics.
In conventional magnetrons there was provided a filter structure, what is called a choke structure, comprising a space formed by a wall of an output-side-sealing metal cylinder the lower end of which is hermetically sealed and electrically connected to the upper end of an anode cylinder, the upper end of which is hermetically sealed to an insulating cylinder, which is concentric with the axis of the magnetron tube and through which a lead for an antenna passes, and a wall of a metal cylinder disposed inside the output-side-sealing metal cylinder, the open end of the space facing the anode of the magnetron as described in Japanese Utility Model Application Laid-open Publication No. 54-125564, for example. FIG. 1 illustrates one example in which there is a cylinder 30 forming a choke structure positioned inside output-side-sealing cylinders 20 and 21 which provides desired fitering characteristics by optimum design of dimensions D to H shown in FIG. 1, D being chosen to be about a quarter of a wavelength to be suppressed, but its prevention of leakage of undesired electromagnetic waves has been unsatisfactory.
In assembling the antenna structure of a magnetron with a conventional choke structure by brazing output-sidesealing metal cylinders 20, 21, a choke-forming metal cylinder 30, an insulator 9, a metal cylinder 10 and an exhaust tube, there were needed jigs for positioning these components from the outside of them as well as jigs inserted into the inside of these components for positioning from the inside of the components. Therefore when using thin washer-shaped Ag-Cu solder for example, positioning jigs placed on the outside of the components sometimes bend the thin washer-shaped Ag-Cu solder interposed between the components without locating the solder into a proper position, resulting in defective brazing and low manufacturing yield rate. In order to solve this problem, an excessive amount of solder was needed. And jigs for positioning from both the outside and the inside of the components were expensive.